The present invention relates to the field of semiconductor device manufacturing. More particularly, it relates to the formation of silicides, including self-aligned silicides (salicides).
Silicides, which are compounds formed from a metal and silicon, are commonly used for contacts in semiconductor devices. Silicide contacts provide a number of advantages over contacts formed from other materials, such as aluminum or polysilicon. Silicide contacts are thermally stable, have lower resistivity than polysilicon, and provide for fairly Ohmic contacts. Silicide contacts are also reliable, since the silicidation reaction eliminates many defects at the interface between the contact and the device feature.
A common technique used in the semiconductor manufacturing industry is self-aligned silicide (salicide) processing. Salicide processing involves the deposition of a metal that undergoes a silicidation reaction with silicon (Si) but not with silicon dioxide or silicon nitride. In order to form salicide contacts on the source, drain, and gate regions of a semiconductor wafer, oxide spacers are provided next to the gate regions. The metal is then blanket deposited on the wafer. After heating the wafer to a temperature at which the metal reacts with the silicon of the source, drain, and gate regions to form contacts, non-reacted metal is removed. Silicide contact regions remain over the source, drain, and gate regions, while non-reacted metal is removed from other areas. Salicide processing is known in the art and described, for example, in commonly assigned U.S. Pat. No. 6,165,903, which is hereby incorporated by reference in its entirety.
Commonly used salicide materials include TiSi2, CoSi2, and NiSi. Although NiSi provides some advantages over TiSi2 and CoSi2, such as lower silicon consumption during silicidation, it is not widely used because of the difficulty in forming NiSi rather than the higher resistivity nickel di-silicide, NiSi2. Even though back end of line (BEOL) temperatures below 500xc2x0 C. can now be achieved, forming NiSi without significant amounts of NiSi2 remains a challenge, since formation of NiSi2 has been seen at temperatures as low as about 450xc2x0 C. Therefore, a method which favors the formation of NiSi and disfavors the formation of NiSi2 is desirable.
According to an embodiment of the invention, a method for forming silicide contact regions on active device regions such as transistor source, drain, and gate regions favors the formation of a first silicide and disfavors the formation of a second silicide.
A first region comprising silicon is formed on a semiconductor substrate. A layer including a metal is formed on the first region, where the metal is capable of forming one or more metal silicides. A suitable material is ion implanted into the layer. A silicide disposed over the first region is formed by the reaction of the silicon with the metal. Prior to silicidation, substantially all of the implanted material may be in the layer, or at least a portion of the implanted material may be in the silicon underlying the layer.
According to an embodiment of the invention, the metal is capable of forming at least a first silicide and a second silicide. The material is soluble in the first silicide, but not the second silicide. In another embodiment, the material is more soluble in the first silicide than the second silicide. As a result, the first silicide is energetically preferred. In one embodiment, the metal is nickel (Ni), the first silicide is NiSi, and the second silicide is NiSi2. The material may include an element chosen from the group consisting of germanium (Ge), titanium (Ti), rhenium (Re), tantalum (Ta), nitrogen (N), vanadium (V), iridium (Ir), chromium (Cr), and zirconium (Zr). The amount of material implanted is sufficient to energetically favor the first silicide but not so great that the material separates from the solid solution. For example, the material may be less than about 15 at. % of the silicide contact region, or between about 5 at. % and about 10 at. %.
After the material is implanted, the temperature of the substrate is raised in order to form a silicide over one or more active regions. The silicide provides a contact so that the active regions can be electrically coupled to other regions, such as metallization lines. The silicide may be a self-aligned silicide, or salicide. The active region may be a source region, drain region, or a gate region. After the silicide is formed, non-reacted metal is removed, for example, by a selective etch process.
According to another embodiment, the material is implanted into the active regions prior to the formation of the metal layer.
According to another embodiment, a layer is formed over silicon-containing active regions, where the layer includes a first material and a second material. The layer may be formed by vapor deposition, such as by evaporation, physical vapor deposition, chemical vapor deposition, laser ablation, or other deposition method.
The first material includes a metal that is capable of forming one or more silicide compounds. The second material may be a material that is soluble in a first silicide of the metal but not in a second silicide of the metal, so that the first silicide is energetically preferred. The second material may be more soluble in the first silicide than the second silicide, so that formation of the first silicide is energetically favored. In one embodiment, the metal is nickel, the first silicide is NiSi, and the second silicide is NiSi2. The material may include an element chosen from the group consisting of Ge, Ti, Re, Ta, N, V, Ir, Cr, Ta, and Zr. The amount of the second material is sufficient to energetically favor the first silicide but not so great that the material separates from the solid solution. For example, the material may be less than about 15 at. % of the silicide contact region, or between about 5 at. % and about 10 at. %.
After the layer is formed, the temperature of the substrate is raised in order to form a silicide over one or more active regions. The silicide provides a contact so that the active regions can be electrically coupled to other regions, such as metallization lines. The silicide may be a self-aligned silicide, or salicide. The active region may be a source region, drain region, or a gate region. After the silicide is formed, non-reacted metal is removed, for example, by a selective etch process.
According to some embodiments of the invention, the silicidation process is a single step, where the temperature of the substrate is raised to a temperature sufficient to form the desired silicide. According to other embodiments, a multi-step process may be used. In a first step, the temperature of the substrate is raised to a first temperature, forming an initial silicide. In a second step, the temperature of the substrate is raised to a second temperature, forming a final silicide.
According to an embodiment of the invention a contact region comprises a first metal silicide and a first material. The first material may be soluble in the first metal silicide but not in a second metal silicide. Alternately, the first material may be more soluble in the first metal silicide than the second metal silicide, so that the first metal silicide is energetically favored. The first metal silicide may be NiSi and the second metal silicide may be NiSi2. The first material may include an element chosen from the group consisting of Ge, Ti, Re, Ta, N, V, Ir, Cr, Ta, and Zr. The amount of the first material is sufficient to energetically favor the first silicide but not so great that the material separates from the solid solution. For example, the material may comprise less than about 15 at. % of the contact, or between about 5 at. % and about 10 at. %.
According to an embodiment of the invention, a contact such as that described above may be part of a semiconductor device, including a substrate with an active region such as a source, drain, or gate region, and a contact disposed over the active region, where the contact may be used to couple the active region to another region such as a metallization line.
A more complete understanding of embodiments of the present invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended drawing that will first be described briefly.